Shades of gray with computer B&W printers is achieved by
changing the dot density. They do not print pixel for pixel.
Rather they print a screen pixel on the page by arraying
multiple printer pixels or dots. HP has a paper describing
the process in their app notes on printing quality. Thus if
the printer uses a 3 by 3 array of printed dots to represent
a single pixel, 9 printed dots would be pure black in their
scheme and no printed dots would be pure white.
I suggest you find someone with an image graphics program
such as Photoshop or you can try GIMP. Open the image file
you have. Then use 'CTRL A' to select all printed pixels on the screen.
Look at the characteristics. I forget if Photoshop uses an
RGB value of 0,0,0 or 255,255,255 to represent all black but
I am willing to bet your image is using an RGB value somewhere
between the two. If that is true, then try changing the color
value used to the extreme 0,0,0 or 255,255,255 whichever
represents pure black and then save the file. Now print it
and your density may improve. Another thing you can do
is to expand a small area of the print to display on the entire
screen till you can see the individual image pixels. You will
likely see the screen pixels are a shade of gray as opposed
to black.
73
Chuck